The present invention relates to an over-voltage protection circuit for protecting a CMOS integrated circuit used in an electric apparatus or an electronic device for automotive, medical or industrial application, or the like, from an over-voltage or surge applied from a power supply. More specifically, the present invention relates to an over-voltage protection circuit that can be formed together with the CMOS integrated circuit on the same semiconductor substrate.
Various over-voltage protection circuits have been used in a control system mounted on a vehicle, and in an electronic part such as an integrated circuit in the control system. The electronic part for the automobile is used in an environment where a power supply voltage tends to vary greatly. Therefore, it is necessary to prevent a malfunction or damage caused by the variation of the power supply voltage.
A conventional over-voltage protection circuit is formed of external elements such as a Zener diode, a resistor and the like mounted to an IC chip to be protected. As a result, due to the Zener diode and resistors, an increased number of parts and extensive labor are needed to assemble the protection circuit, resulting in a higher cost. Recently, an over-voltage protection circuit using a bipolar transistor provided in an IC chip has been proposed (for example, Japanese Patent Publication (KOKAI) No. 06-245,366).
In such a conventional over-voltage protection circuit, an additional process for manufacturing Bi-CMOS is needed, thereby increasing a manufacturing cost. Moreover, the protection circuit includes a large number of elements. Further, in order to accommodate a higher power supply voltage, a large number of elements are required to have a higher breakdown voltage. Accordingly, the protection circuit requires a larger circuit area, thereby making the manufacturing process complicated and increasing a manufacturing cost.
The present invention has been made in view of the problems described above, and an object of the present invention is to provide an over-voltage protecting circuit integrated with an integrated circuit on the same semiconductor substrate, thereby reducing the number of the elements.
Further objects and advantages of the invention will be apparent from the following description of the invention.